Circuits Assembly - December 2007 - (Page 26)

Solder Materials Figure 1. Micrographs after thermal cycling show a SAC 305 J-lead (left) and cobalt alloy J-lead (right). Figure 4. Micrographs of intermetallic layer show the cobalt-enhanced alloy before thermal cycling (left) and after 1,000 cycles (right). Figure 2. Shock test micrographs show the SAC 305 J-lead (left) and cobalt alloy J-lead (right). Figure 5. Micrographs of intermetallic layer show the SAC 305 alloy before thermal cycling (left) and after 1,000 cycles (right). Figure 3. Vibration micrographs show the SAC 305 TSOP (left) and cobalt alloy TSOP (right). Figure 6. X-ray map of copper diffusion in cobalt alloy (left) and SAC 305 (right). boards were then sent to a recognized independent laboratory for testing. Test Parameters Thermal cycling. The IPC-9701A protocol was used. Boards of SAC 305 and the enhanced cobalt alloy were subjected to a thermal range of -10° to +110°C. The number of thermal cycles was 1,000. The temperature rate of change was 10° to 20°C/min. The soak time at each temperature extreme was 5 min. Shock test. The IPC-9701A protocol was used. The shock amplitude and duration was 1500G, 0.5mSec. The number of shocks was five. The direction of shocks was normal to the surface of the printed wiring board (z-axis). Vibration test. IPC-9701A protocol. The frequency range was 20 to 20,000Hz. The vibration amplitude and duration was 15Grms for one hour and 20Grms for one hour. The direction of vibration was all axis simultaneously +3 rotational displacements (6° of freedom). Shear test. A crosshead speed of 0.1 mm/min. with various target components using an Instron 3343 tester. A section of board was placed on a shear test fixture with an immovable edge to hold the target component in place. The Instron crosshead was lowered at a rate of 0.1 mm/min. until the device sheared from the board. Three resistors and five capacitors were sheared from each assembly (SAC 305 and enhanced cobalt). Intermetallic examination and x-ray mapping of the intermetallic. Measurements and photographs were taken of the intermetallic thickness before and after thermal cycling of the cobalt alloy. Pull test. A metal threaded stud was fixed to the top of the IC package and placed in a fixture to hold down the board edges while tensile force was exerted. The force was directly normal to the surface of the board to provide equally distributed force. An Instron 3343 tensile tester pulled the stud at a rate of 1 mm/min. until fracture. The maximum force was recorded for both the cobalt-enhanced and SAC 305 alloys. Temperature/humidity parameters. The Jedec JESD22-A104-B protocol was used. An assembled board soldered with the enhanced cobalt alloy was subjected to temperature and humidity for 500 hr. at temperatures of 85° +/-2°C. Relative humidity was 85% +/-5%. The total test duration was 500 hr. No bias was applied to the board. No monitoring took place until the completion of 500 hr. 26 Circuits Assembly DECEMBER 2007 circuitsassembly.com http://circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - December 2007

Circuits Assembly - December 2007 Contents Caveat Lector Industry News Market Watch Talking Heads Global Sourcing Screen Printing Better Manufacturing Metalization Options for COB Assembly A Test Comparison of SAC and Non-SAC Pb-Free Solders An A-to-Z Guide to X-Ray Inspection BEST: A ‘Funky Chicken’ with an EMS Niche Tech Tips Wave Soldering Process Doctor Pb-Free Lessons Learned Getting Lean Eastern Approaches Product Spotlight Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - December 2007

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